Renato E. de Araujo

Nonlinear optical absorption of antimony and lead oxyhalide glasses

Nonlinear optical properties and optical limiting behavior of antimony and lead oxyhalide glasses were studied using laser pulses of 80 ps at 532 nm. The standard Z-scan technique was used to determine large nonlinear absorption coefficients which range from 11 to 20 cm/GW, using intensities of 100 MW/cm2. Photodarkening was observed when intensities larger than ≈200 MW/cm2 were incident on the samples.

Effectiveness of varnish with CPP-ACP in prevention of caries lesions around orthodontic brackets: an OCT evaluation

OBJECTIVE To evaluate the in vitro efficiency of applying varnish containing casein phosphopeptide (CPP) and amorphous calcium phosphate (ACP) in prevention of caries lesions around orthodontic brackets. MATERIALS AND METHODS For this purpose, brackets were bonded to the vestibular surface of bovine incisors, and eight groups were formed (n = 15) according to exposure of oral hygiene substances and enamel varnish: 1 (control) brushing only performed, 2 (control) brushing + use of mouth wash with fluoride, 3 Duraphat varnish application only (Colgate-Palmolive Ind. E Com. Ltda, São Paulo, SP, Brazil), 4 Duraphat + brushing, 5 Duraphat + brushing + mouth wash, 6 MI Varnish application (GC America, USA), 7 MI + brushing, and 8 MI + brushing + mouth wash. The experimental groups alternated between pH cycling and the procedures described and were kept in an oven at temperature of 37°C. Both brushing and immersion in solutions was performed in a time interval of 1 minute, followed by washing in deionized water three times a day for 28 days of experimentation. Afterwards, evaluation by optical coherence tomography (OCT) of the special type (Ganymede OCT/Thorlabs, Newton, USA) was performed. In each group, a scanning exam of the white spot lesion area (around the region where brackets were bonded) and depth measurement of caries lesions were performed. RESULTS Groups 1 and 3 were shown to differ statistically from groups 5, 6, 7, and 8 (p = 0.000). MI Varnish was shown to be more effective in diminishing caries lesion depth, compared with Duraphat, irrespective of being associated with brushing and mouth wash, or not. LIMITATIONS The major limitation of this study is that it is a study in which demineralization was obtained with the use of chemical products, and did not occur due to the presence of Streptococcus mutans and its acid byproducts. CONCLUSION Application CPP-ACP-containing varnish irrespective of being associated with brushing and mouthwash, or not, reduced depth of caries lesions around orthodontic brackets.

Optical coherence tomography for debonding evaluation: an in-vitro qualitative study.

INTRODUCTION The purpose of this research was to demonstrate the potential of the optical coherence tomography technique on the evaluation of changes and damages in the enamel structure caused by debonding and cleanup procedures. METHODS Twin metal and ceramic brackets were bonded to the labial enamel surfaces of 120 incisors; the brackets were debonded 24 hours later. The anterior surfaces of the teeth were scanned, and optical coherence tomography images were captured in 2-dimensional and 3-dimensional modes before and after debonding and cleanup. A commercial spectral domain optical coherence tomography system with a 5-μm axial spatial resolution was used. The system is based on the Michelson interferometer setup. It is connected to a preconfigured personal computer, and the images are captured with a scanner probe that controls the light beam position at the sample. A total of 960 images were evaluated. RESULTS The analysis of the 2-dimensional and 3-dimensional images obtained with optical coherence tomography allows observation and evaluation of adhesive remnants, enamel damage, and superficial aspects of enamel from different methods of adhesive remnant removal. The 2-dimensional optical coherence tomography analysis allows in-depth observation of the adhesive remnant layer. CONCLUSIONS Optical coherence tomography can be a powerful tool for academic and clinical applications for the evaluation of debonding procedures.

In situ gold nanoparticles formation: contrast agent for dental optical coherence tomography

In this work we demonstrate the potential use of gold nanoparticles as contrast agents for the optical coherence tomography (OCT) imaging technique in dentistry. Here, a new in situ photothermal reduction procedure was developed, producing spherical gold nanoparticles inside dentinal layers and tubules. Gold ions were dispersed in the primer of commercially available dental bonding systems. After the application and permeation in dentin by the modified adhesive systems, the dental bonding materials were photopolymerized concurrently with the formation of gold nanoparticles. The gold nanoparticles were visualized by scanning electron microscopy (SEM). The SEM images show the presence of gold nanospheres in the hybrid layer and dentinal tubules. The diameter of the gold nanoparticles was determined to be in the range of 40 to 120 nm. Optical coherence tomography images were obtained in two- and three-dimensions. The distribution of nanoparticles was analyzed and the extended depth of nanosphere production was determined. The results show that the OCT technique, using in situ formed gold nanoparticles as contrast enhancers, can be used to visualize dentin structures in a non-invasive and non-destructive way.

Automatic real time evaluation of red blood cell elasticity by optical tweezers.

Optical tweezers have been used to trap, manipulate, and measure individual cell properties. In this work, we show that the association of a computer controlled optical tweezers system with image processing techniques allows rapid and reproducible evaluation of cell deformability. In particular, the deformability of red blood cells (RBCs) plays a key role in the transport of oxygen through the blood microcirculation. The automatic measurement processes consisted of three steps: acquisition, segmentation of images, and measurement of the elasticity of the cells. An optical tweezers system was setup on an upright microscope equipped with a CCD camera and a motorized XYZ stage, computer controlled by a Labview platform. On the optical tweezers setup, the deformation of the captured RBC was obtained by moving the motorized stage. The automatic real-time homemade system was evaluated by measuring RBCs elasticity from normal donors and patients with sickle cell anemia. Approximately 150 erythrocytes were examined, and the elasticity values obtained by using the developed system were compared to the values measured by two experts. With the automatic system, there was a significant time reduction (60×) of the erythrocytes elasticity evaluation. Automated system can help to expand the applications of optical tweezers in hematology and hemotherapy.

Long term Raman spectral study of power-dependent photodamage in red blood cells

We monitored time-dependent changes in the Raman spectra of optically trapped red blood cells. By fitting the Raman peaks of individual spectra over time, high-precision time evolutions of peak positions and intensities were obtained. These changes are dependent on the trapping laser power. Characteristic times for these changes were determined for each laser power by fitting the time courses with multi-exponential curves. Raman spectral dynamics showed significant and irreversible changes as a function of trapping duration that we attribute to a combination of photodamage of hemoglobin at short times followed by diffusion of hemoglobin out of the cell at longer times.

Infrared-based system for vehicle classification

This paper presents a low-cost infrared-based system developed for vehicle classification in urban areas. The system contains an equipment that is placed above the roadway and emits down-looking pulsed infrared beams through infrared LEDs (Light-Emitting Diodes). Vehicle profile is obtained detecting and analyzing the infrared light reflected by the vehicle passing directly below the equipment. Profiles of different vehicles were obtained to build a template databank. Vehicle classification is achieved by comparing a vehicle profile with all of the templates. Dynamic Time Warping (DTW) technique is used for carrying out the comparisons. Results obtained are presented and discussed.

Photodynamic inactivation assisted by localized surface plasmon resonance of silver nanoparticles: In vitro evaluation on Escherichia coli and Streptococcus mutans

Localized surface plasmon resonance (LSPR) of gold nanoparticles has been reported to increase the antimicrobial effect of the photodynamic therapy. Although silver nanoparticles (AgNPs) are an efficient growth inhibitor of microorganisms, no studies exploring LSPR of AgNPs to enhance the photodynamic inactivation (PDI) have been related. In this work, we described the LSPR phenomenon of AgNP sand investigated its interaction with riboflavin, a natural photosensitizer. We evaluated the use of AgNPs coated with pectin (p-AgNP) in riboflavin (Rb)-mediated PDI of Escherichia coli (Gram- bacteria) and Streptococcus mutans (Gram + bacteria) using a blue light-emitting diode (λ = 455 ± 20 nm) of optical power 200 mW. Irradiance was 90 mW/cm2 and radiant exposure varied according to the time exposure. Uptake of Rb and p-AgNP by the cells was evaluated by measuring the supernatant absorption spectra of the samples. We observed that LSPR of p-AgNPs was able to enhance the riboflavin photodynamic action on S. mutans but not on E. coli, probably due to the lower uptake of Rb by E. coli. Taken together, our results provide insights to explore the use of the LPRS promoted by silver nanostructures to optimize antimicrobial PDI protocols.

Fiber Optic Sensor with Au Nanoparticles for Dengue Immunoassay

We present a new dengue diagnose method with an all-optical fiber sensor based on LSPR from Au nanoparticles.

TiO2-coated fluoride nanoparticles for dental multimodal optical imaging

Core-shell nanostructures associated with photonics techniques have found innumerous applications in diagnostics and therapy. In this work, we introduce a novel core-shell nanostructure design that serves as a multimodal optical imaging contrast agent for dental adhesion evaluation. This nanostructure consists of a rare-earth-doped (NaYF4 :Yb 60%, Tm 0.5%)/NaYF4 particle as the core (hexagonal prism, ~51 nm base side length) and the highly refractive TiO2 material as the shell (~thickness of 15 nm). We show that the TiO2 shell provides enhanced contrast for optical coherence tomography (OCT), while the rare-earth-doped core upconverts excitation light from 975 nm to an emission peaked at 800 nm for photoluminescence imaging. The OCT and the photoluminescence wide-field images of human tooth were demonstrated with this nanoparticle core-shell contrast agent. In addition, the described core-shell nanoparticles (CSNps) were dispersed in the primer of a commercially available dental bonding system, allowing clear identification of dental adhesive layers with OCT. We evaluated that the presence of the CSNp in the adhesive induced an enhancement of 67% scattering coefficient to significantly increase the OCT contrast. Moreover, our results highlight that the upconversion photoluminescence in the near-infrared spectrum region is suitable for image of deep dental tissue.